This
tortoise has a shell deformity resulting from inadequate calcium
and/or D3 intake. This is an entirely preventable problem.

Obtaining perfect, natural-looking growth in tortoises and turtles is a
multi-factorial challenge. The keeper must balance many different aspects of
diet with extraneous (environmental) factors if this is to be achieved. There
is no ‘quick fix’ or ‘ABC’ method guaranteed to produce reliable results under
all circumstances. Instead, it is vital that keepers understand the basic
mechanisms involved. In this series, we will look in turn at various different
issues that are critical to producing natural, health growth and briefly
discuss how the theory can most effectively be applied in practice.

We will start by looking at calcium, and calcium supplementation.

In nature, tortoises obtain their calcium requirement in several ways. The
bulk of their requirement is typically supplied by consuming calcium-rich
vegetation. This vegetation is itself typically growing on calcium-rich soils,
a situation that leads to plants that are themselves rich in this mineral.
Tortoises also obtain some additional calcium by incidental consumption of
sand/soil particles when feeding, and by deliberately seeking out calcium-rich
items in their environment, such as snail shells or sun-bleached bones.
Surprisingly, even desert environments often have extremely large snail
populations, and it is not unusual to find literally hundreds of estivating
snails per square meter, and thousands of particles of broken snail shell in
the same area. Tortoises have been observed to seek these out,
and to consume them enthusiastically. They provide a concentrated, readily
absorbed source of this vital mineral.

In most captive situations, the gross calcium content of the diet rarely, if
ever, approaches that of wild diets, and the calcium-to-phosphorus ratio of
captive diets is also typically far lower overall than is seen in the wild.
Some typical examples include Plantago sp., with Ca:P ratios of above
20:1 and Opuntia sp., where Ca:P ratios can be as high as 78:1. The
typical diets adopted by many keepers, based upon commercial salads and fruit,
often contain little calcium and an excess of phosphorus.

Opuntia
cacti - a plant typically rich in calcium with a very high Ca:P
ratio. If you keep tortoises, it may be worth cultivating this excellent
food source, as shown here. If we can do it in Wales, UK, you can
do it almost anywhere.

This problem can be addressed in two ways:

1) By carefully selecting diets to include high Ca:P ratio items, and
excluding regular intake of reverse Ca:P items;

2) By careful use of calcium supplements.

In practice, a combination of both methods is recommended. One problem in
relying exclusively upon dietary selection is that many plants that on the
surface appear to offer good, or positive calcium-to-phosphorus ratios, also
contain chemicals that inhibit calcium take-up. Mustard greens, turnip greens,
kale, cabbage, bok choy, spinach, chard and collard greens all fall into this
category. One of the best known examples of such an ‘anti-nutrient factor’ is
oxalic acid. Another is phytic acid, found in high concentrations in peas,
beans and related legumes. It is
therefore necessary to screen diets not only for gross calcium content, and
calcium-to-phosphorus ratio, but also to screen them to exclude reliance upon
plants that contain high levels of these ‘anti-nutrients’. In practice, this is
fairly difficult to achieve on an all-year-round basis.

Calcium supplements

Calcium may be delivered in various forms, some of which are
more readily absorbed and efficient than others. Calcium supplements based on
bone meal are inadvisable due to their inherently high phosphorus content (24%
calcium and 12% phosphorus). As most tortoise diets are already rich in
phosphorus, supplementing with additional phosphorus is neither necessary nor
recommended.

According to a recent review of calcium preparations, there
are at least a dozen common calcium preparations and hundreds of different
formulations available. Calcium carbonate is the most common preparation; some
others include tricalcium phosphate, dicalcium phosphate, bone meal, calcium
citrate-malate, oyster shell, calcium lactate, and calcium gluconate. These
calcium preparations differ in a variety of ways. Calcium carbonate has the
highest concentration of calcium by weight (40%), whereas calcium citrate has
21% calcium and calcium phosphate has 8% calcium by weight. Although calcium
carbonate has the highest concentration of calcium by weight, this form of
calcium is relatively insoluble, especially at a neutral pH. In contrast,
calcium citrate, although containing about half as much calcium by weight, is a
more soluble form of calcium.

In
theory, excessively high intakes of calcium may interfere with the absorption
of other nutrients such as iron and zinc, however, in chelonia we are not aware
that such effects have been demonstrated. Other potential adverse effects of
chronic intakes of high doses of calcium include Hypervitaminosis-D in the case
of supplements containing both calcium and vitamin D. Recent human studies
indicate that increased intake of calcium does not increase risk of kidney
stones. However, restricting dietary calcium may increase urinary excretion of
oxalate which in turn increases risk of kidney stones in addition to causing
bone developmental problems.

As a general rule, calcium carbonate is the preferred source
for use as a routine supplement. It is both safe and effective. Limestone
powder is available at very low cost in bulk from agricultural feed merchants,
and approaches calcium carbonate in efficiency. For emergency use, where
commercial supplements or limestone powders are not available, human calcium tablets
may be ground to a fine powder and applied to the food liberally (note that
while some human calcium tablets may also contain vitamin D, this is usually in
the form of D2 rather than D3 as required by reptiles). Some texts recommend
the use of ground poultry eggshells as a calcium supplement. While it is true
that these do contain useful amounts of calcium (up to 39% available Ca), and
have been shown in human studies to help prevent osteoporosis in mammals, it
should be noted that for chelonian use, there are a number of potential
drawbacks. These include the fact that studies show that such eggshell material
also contains hormone traces (with unpredictable effects upon tortoises) and
that any remaining egg membrane material can also contain antibiotic traces as
well as representing a potential reservoir for contamination by salmonella
organisms. Eggshell derived calcium supplements intended for human use are
extracted and purified under strict laboratory conditions, and are obtained from
poultry on carefully controlled diets. The use of home prepared eggshells from
store-bought eggs is not recommended due to the lack of quality control over
feed inputs and the potential for contamination with residues due to the
difficulty of removing all membrane traces. Cuttlefish bone is a long-standing
method of providing extra calcium to tortoises, and especially to turtles, as
it floats readily in water. The main chemical
constituents of cuttlebone are calcium carbonate, sodium chloride, calcium
phosphate, magnesium salts and an abundance of micro-trace elements. Despite
its high gross calcium content, cuttlefish bone is relatively poorly absorbed,
and as such should not be relied upon as the sole source of calcium
supplementation. It can, however, be employed as a secondary source.

Turtle Blocks

One form of calcium supplement often sold in pet stores is
known as “turtle blocks”. These are mostly made of Plaster of Paris (calcium
sulfate hemi-hydrate) combined with calcium carbonate, often in a 50-50
combination. Plaster of Paris itself contains almost no useable calcium, and is
merely used to adhere the block into shape. Weight-for-weight, therefore,
“turtle blocks” contain 50% or less calcium carbonate, of which, in turn, only
40% may be bioavailable. There are also concerns over heavy metal contamination
in gypsum, from which Plaster of Paris is derived. This is not a form of
calcium supplementation that we therefore recommend.

Recommendations

On balance, the safest and most effective calcium
supplements for routine use with captive tortoises would appear to be a calcium
carbonate based, phosphorus-free ground calcium powder, preferably of
commercial quality, either with or without added vitamin D3. Somespecialist suppliers of reptile vitamin
andmineralsupplements nowoffer products which have been carefully
formulated toprovidea much better match to the specific dietary
requirements of reptiles than standardsupplements, such as Vionate, whichwereoriginally formulated for
general purpose use.One such supplier,
in Britain, isVetarkProductswhoseNutrobalhighcalciumsupplement is especially suitable for herbivorous reptiles. In the United States, Rep-Cal is similarly recommended as a phosphorus-free source
of calcium and D3.

Vitamin
D3

Vitamin D3 plays a pivotal role in bone formation, allowing the body
to absorb calcium, and for maintaining the proper balance of calcium and
phosphorus. A tortoise could eat calcium all day long, but if it was not getting
an adequate amount of vitamin D3, it would not be able to absorb it properly.

In nature, herbivorous tortoises acquire all of their
vitamin D3 requirements as a result of a chemical reaction in the skin,
following exposure to the UV-B spectrum of sunlight. A compound is formed that
is known as 7dehydroxycholesterol (this is sometimes also shortened to 7DCH or
provitamin D). This in turn is converted, by means of temperature, to vitamin D
proper. It is vital that both sufficient UV-B plus adequate basking
temperatures are available if this process is to function properly. This is one
reason why the new UV-B heat lamps (self-ballasted Mercury Vapour lamps) are so
good. They provide both UV-B and the
heat necessary to convert the 7DCH to a form that can ultimately be utilized by
the calcium metabolism. A UV-B fluorescent tube alone will not do this. If such
a tube is used, a separate source of basking heat is mandatory. Without an
adequate source of heat, the conversion will not take place efficiently.

The degree to which you may need to use a supplement containing vitamin D3
will vary according to several factors, principal among these being how far
north you are situated, and the number of hours exposure to natural sunlight
your animals receive or the type and intensity of UV-B supplemental lighting
employed.

As a general rule, if you live in an area where tortoises and turtles occur
naturally and your animals are able to spend at least three or four hours
outdoors in unfiltered sunlight daily, you probably do not need to rely upon
oral D3 supplements. A calcium supplement alone should suffice. If you live in
a northern, cloudy area where tortoises and turtles do not occur naturally, or
your animals’ outdoor time is restricted, it is recommended that you do use a
supplement on a regular basis. We would suggest three times per week as an
absolute minimum. If you provide high output UV-B lamps, and have adequate
basking facilities, you may be able to rely upon these to promote adequate D3 synthesis
but personally, I would prefer to hedge my bets by supplementing with a
combined calcium and D3 supplement orally at least twice a week.

Calcium and Vitamin D3 are certainly not the only components required to
facilitate healthy bone development in tortoises and turtles:

• Magnesium is essential for proper calcium absorption and is an important
mineral in the bone matrix. It has specific effects on the parathyroid hormone,
which helps regulate proper calcium metabolism.

• Phosphorus is the second most prevalent mineral in bones and makes
up more than half the mass of bone mineral. Thus, the diet needs to have
sufficient phosphorus in order to build healthy bones. For most tortoises and
turtles, this is not a problem, as most vegetation is rich in this element.
When phosphorus levels in the blood are too high, however, the body takes calcium
out of the bones to bind with the phosphorus to facilitate its removal from the
bloodstream. Bones can become brittle or deformed as a result.

Many other micro trace elements are also important, including Manganese,
Zinc, Boron and Strontium. These may not be provided by a regular calcium or
calcium with D3 supplement alone. An appropriate and varied diet will certainly
provide most of them, but a wide-range mineral supplement can also be used to
ensure that they are present on a regular basis. We would recommend such a
supplement be used no more than once weekly.

To summarise, in order to provide the calcium that tortoises and turtles
need, especially during growth phases or for egg-laying females:

Try to provide a diet that provides an overall positive
calcium-to-phosphorus ratio

Do not rely on items rich in oxalates, phytates or other calcium-inhibiting
compounds

Use a phosphorus-free calcium supplement daily

Carefully consider vitamin D3 requirements. Provide access to adequate
levels of natural sunlight, use an adequate and correctly installed and
maintained artificial UV-B source, or provide an oral D3 supplement at least 3
times per week.

Provide a general broad spectrum mineral trace element supplement (such as
Vionate) once per week.

Available from Carapace
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